High Efficiency Video Coding (HEVC) is a new coding standard that has been developed in recent years. In the High Efficiency Video Coding (HEVC) system, the fixed-size macroblock of H.264/AVC is replaced by a flexible block, named coding unit (CU). Pixels in the CU share the same coding parameters to improve coding efficiency. A CU may begin with a largest CU (LCU), which is also referred as coded tree unit (CTU) in HEVC. In addition to the concept of coding unit, the concept of prediction unit (PU) is also introduced in HEVC. Once the splitting of CU hierarchical tree is done, each leaf CU is further split into one or more prediction units (PUs) according to prediction type and PU partition.
In the current development of range extension (RExt) or screen content coding for High Efficiency Video Coding (HEVC) standard, some tools have been adopted due to their improvements in coding efficiency for screen contents. For Intra blocks, Intra prediction according to the conventional approach is performed using prediction based on reconstructed pixels from neighboring blocks. Intra prediction may select an Intra Mode from a set of Intra Modes, which include a vertical mode, horizontal mode and various angular prediction modes. For HEVC Range Extension and screen content coding, a new Intra coding mode, named Intra-block copy (IntraBC) has been used. The IntraBC technique that was originally proposed by Budagavi in AHG8: Video coding using Intra motion compensation, Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 13th Meeting: Incheon, KR, 18-26 Apr. 2013, Document: JCTVC-M0350 (hereinafter JCTVC-M0350). An example according to JCTVC-M0350 is shown in FIG. 1, where a current coding unit (CU, 110) is coded using Intra MC (motion compensation). The prediction block (120) is located from the current CU and a displacement vector (112). In this example, the search area is limited to the current CTU (coding tree unit), the left CTU and the left-left CTU. The prediction block is obtained from the already reconstructed region. Then, the displacement vector, also named motion vector (MV), and residual for the current CU are coded. It is well known that the HEVC adopts CTU and CU block structure as basic units for coding video data. Each picture is divided into CTUs and each CTU is reclusively divided into CUs. During prediction phase, each CU may be divided into multiple blocks, named prediction units (PUs) for performing prediction process. After prediction residue is formed for each CU, the residue associated with each CU is divided into multiple blocks, named transform units (TUs) to apply transform (such as discrete cosine transform (DCT)).
In JCTVC-M0350, the Intra MC is different from the motion compensation used for Inter prediction in at least the following areas:                MVs are restricted to be 1-D for Intra MC (i.e., either horizontal or vertical) while Inter prediction uses 2-D motion estimation.        Binarization is fixed length for Intra MC while Inter prediction uses exponential-Golomb.        Intra MC introduces a new syntax element to signal whether the MV is horizontal or vertical.        
Based on JCTVC-M0350, some modifications are disclosed by Pang, et al. in Non-RCE3: Intra Motion Compensation with 2-D MVs, Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 14th Meeting: Vienna, AT, 25 Jul.-2 Aug. 2013, Document: JCTVC-N0256 (hereinafter JCTVC-N0256). Firstly, the Intra MC is extended to support 2-D MVs, so that both MV components can be non-zero at the same time. This provides more flexibility to Intra MC than the original approach, where the MV is restricted to be strictly horizontal or vertical.
In JCTVC-N0256, two MV coding methods were disclosed:                Method 1—Motion vector prediction. The left or above MV is selected as the MV predictor and the resulting motion vector difference (MVD) is coded. A flag is used to indicate whether the MVD is zero. When MVD is not zero, exponential-Golomb codes of the 3rd order are used to code the remaining absolute level of the MVD. Another flag is used to code the sign.        Method 2: No Motion vector prediction. The MV is coded using the exponential-Golomb codes that are used for MVD in HEVC.        
Another difference disclosed in JCTVC-N0256 is that the 2-D Intra MC is further combined with the pipeline friendly approach:                1. No interpolation filters are used,        2. MV search area is restricted. Two cases are disclosed:                    a. Search area is the current CTU and the left CTU or            b. Search area is the current CTU and the rightmost 4 column samples of the left CTU.                        
Among the proposed methods in JCTVC-N0256, the 2-D Intra MC, the removal of interpolation filters, and the search area constraint to the current CTU and the left CTU have been adopted in a new version draft standard. The CU level syntax corresponding to JCTVC-N0256 has been incorporated in High Efficiency Video Coding (HEVC) Range Extension text specification: Draft 4 (RExt Draft 4), Flynn, et al., Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 14th Meeting: Vienna, AT, 25 Jul.-2 Aug. 2013, Document: JCTVC-N1005.
It is desirable to further improve the performance of IntraBC mode. Furthermore, it is desirable maintain any new development within the same framework of existing HEVC standard.